Local area networks, LANs, have been designed with many different addressing schemes. For example, the Ethernet LAN design, IEEE 802.3 standard, has 47 bits designated for multicast addresses for a total of approximately 140 trillion addresses.
In contrast, implementations of the token ring IEEE 802.5 standard provide only approximately 24 to approximately 31 separate addresses for multicast addresses, and these addresses are provided in the functional addressing defined by the IEEE 802.5 standard. The IEEE 802.5 standard provides 6 bytes, or 48 bytes, for functional addressing, but chips implementing the standard first require a few of the bits to be set to a defined value, referred to as the Functional Address Indicator, and also require that only one bit of the remaining bits be set to "1", and the others be set to "0". The bits having the defined value give an indication that the rest of the bits indicate a "functional address", and the "rest of the bits" is only approximately 24 to 31 bits depending upon the implementation, and only one of these bits can be set.
It is a common practice to develop applications programs to run in a station on a LAN, and to address the the applications program by use of a multicast address in the DA field of the MAC header. When the station detects a frame having a predetermined multicast address in the DA field of the MAC header, the applications program is caused to execute.
A difficulty with applications programs designed to execute, upon receipt by the station of a frame having having a predetermined multicast address, is that in a local area network such as the IEEE 802.5 token ring there are enough multicast addresses. Only approximately 31 multicast addresses are available in the IEEE 802.5 token ring LAN, and these are known as "functional addresses".
A solution to the mapping of multicast addresses onto functional addresses of LANs having inadequate multicast address capability has been suggested in U.S. Pat. No. 4,933,938, issued to D. B. Sheehy on Jun. 12, 1990. In the Sheehy patent a translation table is used to directly map the multicast addresses of the first LAN onto the multicast addresses of the second LAN.
However, there still remains the problem of using applications developed for some LANs such as IEEE 803.3 Ethernet, having approximately 140 trillion multicast addresses, on and other LANs such as the token ring IEEE 802.5 standard LAN, having only approximately 24 to 31 multicast addresses in their functional address space. Accordingly, many applications developed for the Ethernet 803.3 LAN or the ANSI/IEEE FDDI token ring LAN cannot be used in a station on an IEEE 802.5 token ring LAN.